The present invention relates generally to processing apparatuses, and more particularly to a processing apparatus that transfers a pattern on a mold as an original onto a substrate such as a wafer. The present invention is particularly suitable for a processing apparatus that uses the nanoimprint technology.
The nanoimprint technology is one alternative to the photolithography that uses the ultraviolet (“UV”) light, X-rays and electron beams to form fine patterns for semiconductor devices. The nanoimprint presses (or stamps) a model (or a mold), on which a fine pattern has been formed by the electron-beam exposure etc., against a substrate such as a wafer to which a resinous material (resist) is applied, thereby transferring the pattern onto the resist. See, for example, S. Y. Chou, et al., Science, Vol. 272 pp.85-87, 5 Apr., 1996. It is already demonstrated that the nanoimprint can transfer a fine shape of about 10 nm, and attracts attention especially as a fine periodic pattern forming means for magnetic recording media. Active researches and developments are globally under way.
The nanoimprint sometimes uses the vacuum environment to prevent intrusions of air bubbles between a mold and a substrate. Methods that facilitate the resist flow at the press time include a (heat cycle) method of heating polymer as the resist more above the glass transition temperature for transfer, and a (photo-curing) method of exposing and curing the UV curable resin as the resist while pressing it with a transparent mold, and of releasing the mold.
A manufacture of semiconductor integrated circuits (“ICs”) requires an overlay that transfers the next pattern with a precise alignment with a circuit pattern already formed on a substrate. The heat cycle method heats the resist, causes the substrate and mold to thermally expand with a temperature rise, and has difficulties in maintaining the overlay accuracy. Accordingly, the photo-curing method, in which temperature control is relatively easy, is more suitable in applying the nanoimprint to the manufacture of the semiconductor ICs.
For the minimum critical dimension (“CD”) of a semiconductor IC pattern of 100 nm or less, the resist requires a low-viscosity material to fully fill in the mold's fine structure. A nanoimprint apparatus typically successively transfers a pattern onto a wafer surface in a step-and-repeat manner. Here, the “step-and-repeat manner” is one mode of exposure method that moves a wafer stepwise to an exposure area for the next shot every shot of cell projection onto the wafer. However, due to the low viscosity of the resist, it is difficult to previously apply resist to a substrate, transport and mount the substrate as in an exposure apparatus. One proposed method drops a proper quantity every time the mold is pressed in transferring each shot. See, for example, M. Colburn, S. Johnson, M. Stewart, S. Damle, T. Bailey, B. Choi, M. Wedlake, T. Michaelson, S. V. Sreenivasan, J. G. Ekerdt and C. G. Willson. “Step and Flash Imprint Lithography: A new approach to high resolution patterning.” Proc. SPIE 3676 (I): 379 (1999).
The mold includes plural patterns for plural chips, and generally has a rectangular shape, whereas a wafer has a circular shape. Therefore, in transferring a mold pattern matrix-wise onto a wafer, the mold outstretches the wafer's peripheral shot (referred to as a “peripheral shot” hereinafter) that is smaller than the mold size, thus resulting in a partial transfer of the mold pattern. The partial transfer of the mold pattern to the peripheral area is economical and beneficial because some of the plural chip patterns in the mold are transferred.
However, the low-viscosity resist flows out from the peripheral shot, and contaminates the processing apparatus and the wafer chuck for fixing the wafer. Thus, uneconomically, the prior art cannot transfer the mold pattern to the peripheral shot.